A conventional method for producing an α particle emitter involves sandwiching an α emitter between cover members to seal for use in a smoke detector, rolling and stretching it with the cover members and cutting them into a predetermined shape to complete when a predetermined density in the number of atoms was reached. Other methods have been proposed (see, for example, Patent Document 1: Method for Collecting Radon), in which metal atoms serving as an α emitter are trapped in a solution state by cooling trapped radon gas with liquid nitrogen to cooling trapped radon gas with liquid nitrogen to liquefy it.
Patent Document 1: Japanese Patent Application Laid-Open No. 2002-265206